The invention relates to a solid state imaging device comprising a system of sensor elements arranged in rows and columns for converting radiation into electric charges which can be transported parallel to the column direction by vertical transport means to a horizontal readout register in the form of a charge-coupled device into which the charges are entered row by row and subsequently read out at an output of the horizontal register during a certain time interval, called active line time hereinafter, means being present by which the device can be set in either of two states, whereby in a first state the signals from all columns of the system are used and in the second state the signals from a number of columns are not used. The invention also relates to a camera provided with such an imaging device.
The device may in this case be formed by a monolithically integrated circuit in which the sensor elements in the form of photodiodes or MOS diodes are accommodated together with the vertical transport means and the horizontal readout register in a common semiconductor body made of, for example, silicon. The vertical transport means are usually formed by charge-coupled devices which either coincide with the photosensitive elements, such as, for example, in the case of frame transfer sensors (FT sensors), or are provided interposed between columns of separate photosensitive elements (interline sensors). In alternative embodiments, the photosensitive elements and the horizontal register may be manufactured in different semiconductor bodies, for example, when requirements are set for the photosensitivity which are not compatible with the requirements set for the readout register. It is noted here that the terms "horizontal" and "vertical" are to be understood in a relative sense only, not in an absolute sense, merely indicating that the transport in the readout register is transverse to the transport by the said transport means.
The possibility of effectively switching off a number of columns renders it possible to obtain an imaging device which satisfies the requirements of different standards, so that it is not necessary to design an adapted device and/or camera separately for each standard.
U.S. Pat. No. 4,426,664 discloses a charge-coupled imaging device of the kind mentioned in the opening paragraph which can be used both in the NTSC system and in the PAL or SECAM system. The imaging device is for this purpose provided with as many rows and columns as are necessary for use in the PAL or SECAM system. For use in the NTSC system, a number of lines as well as a number of columns are not used in that the electric charge generated in the relevant columns is drained off instead of being processed further as video information. For this purpose, the readout register is coupled at one end, i.e. the left-hand end, to an output terminal where the video information can be derived, and at the opposite end, so the right-hand end, to a drain for draining off the information which is not used. This charge is generated in a strip of columns at the right-hand side of the imaging device. During operation in the NTSC setting, a full line including the unnecessary charge packages from the strip of columns mentioned above is transported into the readout register each time. The active video information is transported to the left during the active line time in order to be read out. Simultaneously, the transport direction is reversed in the portion of the readout register in which the non-active information is stored, so that the relevant charge can be drained off at the right-hand end of the readout register.
One of the disadvantages of such a device is that the optical center in at least one of the two states does not coincide with the center of the portion of the imaging device which is in use. The luminous intensity is generally highest in the optical center in a system of lenses, such as in a camera, and decreases towards the edges to a value which is visibly lower at the edges. A similar profile is often found in the resolution of the optical system. This non-uniform intensity, possibly coupled to a decreasing resolution, is not unpleasantly noticeable during display as long as the intensity and the resolution are highest in the center of the displayed picture. If, however, the centers do not coincide, as is the case in the imaging device described above, the intensity maximum, and possibly the resolution maximum, will not lie in the center during picture display, which will in general be felt to be very unsatisfactory.
Such problems may also occur in situations other than that described above, when the information from a number of columns is not used. Thus it is very important for the optical center of the lens to coincide always with the center of the imaging device when a zoom lens is used.